The invention relates to a heat exchanger, in particular an oil cooler for motor vehicles. Various designs are known of oil coolers for motor vehicles, i.e., engine oil coolers or transmission oil coolers. Air-cooled engine oil coolers are arranged in the front engine compartment of the motor vehicle and are cooled by ambient air. Transmission oil coolers are often accommodated in the coolant tanks of the coolant coolers (radiators) and are therefore cooled by the coolant of the engine cooling circuit. Also known are so-called laminate oil coolers, as described for example in the EP-A 932 011. The flow passages for the oil in this case are formed by pairs of laminar plates which comprise two plates connected on their circumferential edges by means of a continuous fold. Metal turbulence inserts are placed between the plates and are brazed to the plates. At their ends, the elongated plates have apertures which are in each case connected to one another to form a distributor manifold and a collection manifold, respectively, which have oil inlet and outlet connection pieces. The laminate oil cooler is arranged in a coolant tank made from plastic and is connected to a transmission oil circuit via the oil inlet and outlet connection pieces. The individual plates are held spaced apart by intermediate rings and/or studs and form a stack through which coolant can flow. All the parts of the laminate oil cooler which consist of aluminum or stainless steel are brazed together. This requires accurate manufacturing with very small tolerances of all the parts which are to be joined; these parts are generally clad with a brazing material. Furthermore, this mode of design also requires a large number of individual parts.
A similar design of laminate oil coolers has been disclosed in U.S. Pat. No. 5,538,077, in which elongate plate pairs are in each case constructed from two plates with a metal turbulence plate between them, and these parts are brazed to one another at their circumferences. At the ends of the plate pairs there are apertures for supplying and discharging the oil. The apertures are brazed together by means of stamped formations and are thereby formed into distribution and collection manifolds, so that oil can flow through the entire stack of plate pairs in parallel. On the secondary side, the plate pairs, which in each case form gaps between them as a result of the provision of studs, have coolant flowing through them. This known laminate oil cooler also has the drawback of requiring a large number of parts and relatively high manufacturing costs.
JP-A 11-142074 likewise discloses a laminate oil cooler which is arranged in a metallic coolant tank of a radiator and is cooled by engine coolant. Apertures, in which slotted tubes for supplying and discharging the oil are arranged, are provided at the end sides of the plate pairs. The laminate oil cooler can be brazed together with its connection tubes and the coolant tank.
Another design of oil cooler is characterized by flat tubes, as described, for example, in EP-A 444,595, which is commonly assigned with the present application. The flow passages for the oil are in this case formed by flat tubes produced from an aluminum or steel sheet and are welded by means of longitudinally running weld seams. A turbulence insert is introduced into the closed flat tube and brazed to the flat tube, which may be clad with a brazing composition, in order to increase the resistance to internal pressure. Apertures are provided at the ends of the flat tubes and are connected to the apertures of adjacent flat tubes, so as to form in each case one distribution manifold and one collection manifold for the oil. Unlike in the case of the laminate oil coolers, the flat tubes have to be closed at their ends. In the case of the known flat tube oil cooler, this is done by means of an end-side fold, which has a corrugated contour in order to increase the rigidity. In the case of air cooling, a suitable arrangement of fins is provided between the flat tubes.
A further flat tube oil cooler has been disclosed by DE-A 196 05 340, also commonly assigned, wherein the flat tubes are closed off at their ends by a solid insert part. One problem with the flat tube design is that, unlike in the case of the laminated oil coolers, it is difficult to apply the compressive force required to braze the turbulence inserts and the end closure insert part. If the pressure is insufficient, the brazing gaps are too large and brazing is incomplete, which leads to leaks or “swelling” in the flat tubes.